Yet, the above equipments necessarily comprise storage areas, either for liquid hydrocarbons (fuels, solvent and similar products), or for liquefied gaseous hydrocarbons. For transporting such dangerous products from one site to another of the storage areas and for counting such dangerous products, it has been necessary to use units comprising various pumps and measuring apparatus which are electrically supplied through a plurality of cables from one of more panels placed in premises which can be a particular building of a plant, or still a kiosk or a boutique for stations open to the public.
These equipments are particularly complicated in self-service delivery stations since it then exists all a transmission net through a plurality of cables connecting together the delivery apparatus to the central unit situated in the boutique or kiosk.
As this is well known, each delivery station necessitates to be connected to tubes for the products to be delivered as well as to supply cables and transmission cables for transmitting information given by each pumping and measuring unit.
In order to design units having a nice appearance, all these cables are placed under the ground in passages, ducts, sheaths, or sleeves and nozzles of sizes corresponding to the number of cables and their respective cross sections.
There is already known to provide from place to place junction holes and cable pulling holes in order to permit changes in direction of the nests or a control of the cables when cables of great lengths are used between the delivery stations and the central station.
The corresponding equipments make to communicate through an underground nest of cables, each pumping and measuring apparatus comprising at least one electric motor, with a general control cabinet in premises where is permanently placed an agent looking after at least one central display unit in case of self service, but in these premices there also exists for the comfort of the staff, some gaseous product protected apparatus for example electrical heating apparatus, convectors or air-conditioners.
However, despite all the protections which are taken, it may come that leakages or seepages are produced along the pipes or fittings of the hydraulic part within the delivery station containing the pumping and measuring unit.
The products being extremely volatile, it happens that gaseous products can very rapidly accumulate in the above mentioned holes, passages and ducts or in the sheaths sleeves and nozzles, and, thus, these gaseous products will come to the control premises.
There is therefore very rapidly made an explosive mixture which is very dangerous not only because its toxicity but above all because of blasting risks in case of a flame, an electrical contact making a spark, a hot point and even any static electrical charge able to be produced on the ground surface around the station.
The result is obviously an explosion of the explosive mixture with sometimes accidents on people.